Letoff mechanism for looms



Oct. 17, 1950 R. e. TURNER 2,526,303

LE'I'OF'F MECHANISM FOR LOOMS Filed D80. 50, 1948 2 Sheets-Sheet 1 INVENTOR RICHARD G. TURNER ATTORNEY.

Oct. 17, 1950 TURNER 2,526,303

LETOFF MECHANISM FOR LOOMS Filed Dec. so, 1948 .2 sheets-sheet 2 INVENTOR.

85 9| RICHARD cs. TURNER ATTORNEY.

Patented Oct. 17, 1950 LETOFF MECHANISM FOR LOOMS Richard G. Turner, Worcester, Mass., assignor to Crompton & Knowles Loom Works, Worcester, Mass, a corporation of Massachusetts Application December 30, 1948, Serial No. 68,292

Claims.

This invention relates to improvements in letoff mechanisms for looms and it is the general object of the invention to provide control means for the letoff which will insure smooth operation thereof.

In order to maintain proper tension in the warp threads of a loom it is necessary that the letoif mechanism exert uniform resistance to the forward movement of the warp threads. Many forms of letoif provide this resistance by means of weights which, however, vibrate considerably during loom operation with the result that the tension in the warp thread varies.

It is an important object of the present invention to provide a letoif with pneumatic tension means which is not materially affected by the operation of the loom, thereby insuring a smoother operation and a more uniform tension in the warp.

As the diameter of the yarn on a warp beam decreases it is necessary to reduce the resistance to turning of the beam, since the latter requires a larger angular movement per pick of the loom, and it is a further object of the invention to provide a control for the pneumatic system of a letoff mechanism which will permit variation in the resistance ofiered to turning of the warp beam.

If a loom is stopped temporarily as the result of breakage of either a warp or a weft thread it is desirable that the rearward tension of the warp be maintained, and it is a further object of the invention to control the pneumatic system for the letoif mechanism in such manner that it will operate while the loom is temporarily at rest. This result may be accomplished by a pump or fan for the system operated by the loom motor and continuing to create pneumatic pressures so long as the motor is in operation.

When the loom is stopped for longer periods during which the motor is not operating it is desirable to be able to maintain a rearward force on the warp threads and it is a still further object of the invention to effect this result by means of a valve or the like which will automatically close the system to prevent changes of pneumatic pressures therein except for minor leakages during extended periods of loom stoppage.

In the weaving of certain fabrics so-called barre or bar marks occur extending across the cloth at irregular intervals along its length. These marks reduce the value of the cloth and are likely to be formed when the warp tension is above normal. It is sometimes difficult to determine What part of the loom causes these marks and the variation in warp tension which is thought to cause them. It is believed, however, that some of the marks are caused by faulty operation of the let-off, especially those operating with weights acting to exert a rearward force n the warp threads.

At each beat-up of the lay a forward force is exerted on the warp the effect of which is to lift the usual weights. After the lay passes front center this force is diminished and the weights fall. If before the weights reach their normal low position another beat-up occurs the tension in the warp is determined by the kinetic energy of the falling weight which is greater than the static or potential dead weight which they would exert if at rest. The second pick is therefore beat in very close to the previous pick, and if this condition exists for several picks a bar mark will be produced. This efiect is likely to occur where there is some rhythmic relation between the falling of the weights and the beat-up rate of the lay.

It is another object of the invention to eliminate the weights and in their place substitute a pneumatic tensioning means in which a large part of the kinetic energy of moving weighted parts or masses is eliminated. The elasticity of the air in the pneumatic cylinder also cushions sudden changes and furthermore permits a greater or quicker responsiveness to temporary increases in tension of the warp than is possible where Weights are employed. The rise and fall of air pressure in the pneumatic system is not accompanied by complications due to kinetic energy, momentum and inertia of weights such as is found in the usual letoff mechanism.

With these and other objects in View which will appear as the description proceeds, the invention resides in the combination and arrangement of parts hereinafter described and set forth.

In the accompanying drawings, wherein the invention is shown applied to two different types of letoff mechanism,

Fig. 1 is a plan view of the rear part of the loom having the invention applied to the preferred form of letoff,

Fig. 2 is a side elevation looking in the direction of arrow 2, Fig. 1, with the main shaft of the loom in cross section,

Fig. 3 is an enlarged vertical section on line 3-3 of Fig. 2,

Fig. 4 is a vertical section on line 4-4 of Fig. 1,

Fig. 5 is an enlarged view showing the structure illustrated at the lower right hand part of Fig. 4.

Fig. 6 is an enlarged detailed vertical section on line @-6, Fig. 5,

Fig. 7 is an enlarged vertical section on line 1-4, Fig. 1, showing one of the control valves, and

Fig. 8 is a modified form of the invention showing the same applied to a different type of letoff mechanism. Referring particularly to Figs. 1 and 2, the loom frame it is provided with top and bottom shafts H and [2, respectively, which are connected by gears 13 and Hi, respectively. A gear 15 freely rotatable on the top shaft ii is driven by an electric motor l6 supported by a bracket 11 on the loom frame. By means of clutch mechanism controlled by a lever IS the motor and gear l5 can be coupled in driving relation with the top shaft I I. Shipper and brake handles [8 and I9 of usual construction are provided to start and stop loom operation.

The warp beam B is mounted for rotation in bearings 28 one of which is shown in Fig. 4 and the warp W leads upwardly from the beam over a whip roll 2! and then forwardly to the weaving instrumentalities. In the preferred form of the invention the whip roll is mounted on upright levers 22 pivoted as at 23 to a support bracket 24 extending rearwardly from the loom frame. Lever 22 engages levers 25 which are connected together by a link 26 and another link 21 connects link 26 to a lever 28 pivoted at 28.

When the lever 28 is pulled down it rocks the levers 25 in a clockwise direction as viewed in Fig. l to exert rearward force on the upright levers 22 and thereby move the whip roll rearwardly. The forward advance of the warp and cloth effected by the take-up mechanism not shown tends to turn the warp beam B in a clockwise direction as viewed in Fig. 4, and when the beam is held against rotation the whip roll moves forwardly or to the right, Fig. i.

Rotation of the warp beam B is controlled by an escapement mechanism shown more particularly in Fig. l. The beam has secured thereto a gear 38 meshing with a pinion 3i fast with a gear 32 which meshes with a pinion 33. A gear 36 fast with pinion 33 meshes with a pinion fast with a star or escapement wheel An escapement lever 31 pivoted at 38 controls rotation of the escapement Wheel 33 and is adapted for engagement with a brake shoe 39 on a brake lever 49].

A rod il connected to lever 28 extends downwardly through the forward or right end of lever 46 as viewed in Fig. 4, and a compression spring 4-2 surrounding rod a! engages the top of the forward arm of lever 40.

When lever 28 is in its down position it causes spring 62 acting through lever ie to hold the brake shoe 39 against the escapement lever 37, thereby preventing rotation of the star wheel and the gears and pinions connected thereto, and the warp beam B will be held against rotation. When lever 28 rises the brake shoe 39 will be moved away from the escapement lever 37 by a collar 43 on rod 4! under the forward arm of lever 49. Under these conditions the escapement wheel can turn and the force exerted by the warp is able to turn the beam B, thereby slackening warp tension and permitting the whip roll 2| to move rearwardly with resultant downward motion of lever 28.

The matter thus far described in connection more particularly with Fig. 4 may be substantially the same as that shown in prior Patent 4 No. 2,330,514. As shown in that patent weights tending to move the whip roll rearwardly are suspended from lever 28, but as already mentioned these weights vibrate during loom operation with the result that there is a variation in the tension of the warp threads.

In the preferred form of the invention the weights are replaced by a pneumatic system which acts to create a uniform downward force on lever 28. This system includes a cylinder 56 mounted in fixed position on a support 5| and having a piston 52 therein connected to a link 53 extending upwardly to and operatively connected to lever 28.

An air pump P mounted in stationary position as suggested in Fig. 2 is driven by a belt 55 which in turn is driven by a belt 56 extending around a pulley 57 on the motor l6. Whenever the motor is operated subatmospheric pressures are created within a pipe 58 connected as shown in Fig. 3 to the pump. The air drawn out of pipe 58 is discharged through an exhaust 59.

Pipe 58 extends across the loom to a fitting 68 having a port 5! which communicates with the lower interior part of the cylinder 50. This port can be closed by a slide valve 62 normally held in the position shown in Fig. 5 by a solenoid 63 which will be energized so long as the motor I5 is running. When the circuit for the motor is opened to stop operation thereof the solenoid becomes deenergized and a compression spring surrounding stem 65 of the slide valve 62 causes the latter to move to the left, Fig. 5, to close port 61.

Leading upwardly from the fitting 60 is a pipe or tube iii connected to a valve 'H which in turn is connected to a pressure gauge 12 by a pipe 13. The valve ii, shown more particularly in Fig. '7, is manually adjustable and has a needle I5 which controls the amount of air which can be drawn or leak into the system through an orifice '16.

Under normal conditions when the loom is operating the pump P will create subatmospheric pressures in the cylinder 50 below the piston 52 to exert a downward force on the latter and link 53 which tends to move lever 28 downwardly. When the escapement wheel 35 is locked the whip roll will move forwardly graduall and thereby lift lever 28 against the force of the subatmospheric pressures below piston 52. As soon as upward movement of lever 28 effects release of the escapement wheel the beam will turn and the whip roll will move rearwardly by a force depending upon subatmospheric pressures below piston 52.

The gauge 72 will indicate the amount of subatmospheric pressures in the system and this pressure can be regulated by manipulation of the needle 75 by means of a hand wheel 7! of a small shaft 78 part of which is threaded into the valve at 79, see Fig. '7. If the pressure is too great the needle is backed off to permit leakage into the pneumatic system, thereby lowering the pneumatic force tending to efiect downward movement of piston 52 in cylinder 50, and conversely, turning needle 75 into orifice or passage '36 increases the pneumatic pressure. As the diameter of the warp on the beam decreases the needle can be turned into the orifice to reduce leakage into the system. When the beam has a large diameter of yarn thereon the needle can be backed out of the orifice to increase leakage.

he modified form of the invention shown in Fig. 8 is used with a cliiferent form of letoff mechanism wherein the warp beam B is controlled by letoff mechanism such as that shown in prior Patent No. 1,803,143. A segment 80 rotatable about the axis of the warp is connected to a link Bl which leads downwardly to a cylinder 82 similar to cylinder 50. A piston 83 is connected to the bottom of link 8| and when drawn downwardly due to subatmospheric pressures in cylinder 82 moves the segment 80 in a counterclockwise direction as viewed in Fig. 8.

Cylinder 82 is provided with a fitting 85 similar to fitting 60, and pipes 86 and 81 perform the same function in the modified form of the invention as do their corresponding pipes 58 and 10 in the preferred form. A valve 83 similar to valve II is used in the modified form of the invention and a gauge 89 similar to gauge '12 may also be used. Solenoid 90 and valve 9| are similar to parts 63 and 62 of the preferred form.

The pneumatic system set forth in Fig. 8 creates a uniform downward pull on link BI, and as beam B turns in a clockwise direction, Fig. 8, the piston 83 rises in cylinder 82 until a periodically rocking lever 92 engages a pin 93, whereupon the segment 80 has a retrograde movement, or moves in a counterclockwise direction, due to piston 83, until pin 93 moves out of the range of operation of lever 92. The operation is then repeated with resultant upward movement of the link 8| against the pneumatic forces of the system until pin 93 is again in position to be engaged by lever 92.

In the form shown in Fig. 8 valve 88 will be manipulated to increase leakage into the system as the warp diameter on the beam decreases. In both forms of the invention the gauges can be utilized to enable the weaver to control the amount of leakage of air into the pneumatic system as the diameter of the warp on the beam decreases. In the preferred form of the invention the downward pull of piston 52 is gradually increased as the warp diameter diminishes and this will be accomplished by diminishing the leakage into the system with resultant increase in pneumatic pressures which will be indicated by the gauge 12. In the modified form of the invention, on the other hand, leakage into the system is decreased as the warp diameter diminishes, and in a similar manner gauge 89 can be utilized to regulate the amount of decrease. Changes in the control valves 11 and 88 can be made at regularly recurring intervals and by gradations which will ordinarily be finer than is possible when weights are used as heretofore.

From the foregoing it will be seen that the invention sets forth a simple form of a letoif mechanism for the purpose of maintaining uniform tension in the warp threads. The subatmospheric pressures for the system are produced by a pump which operates whenever the driving motor for the loom is running. Furthermore, means are provided for controlling the amount of leakage into the pneumatic system so that the subatmospheric pressures can be varied. Also, upon stoppage of the motor a valve normally open during motor operation automatically closes the system to maintain subatmospheric pressures below the piston on the cylinder and thereby preserves tension of the warp threads. Also, the weight of the piston and its connectors is very much less than that of the usual weights employed in letoffs with the result that the kinetic energy of the moving parts is greatly reduced and there is less likelihood of the production of barre. The gaseous pressure within the piston also permits an elasticity or responsiveness to variations in warp tension which cannot be attained where weights are employed. While the invention has been described in connection with subatmospheric pressures the invention is not necessarily thus limited.

Having thus described the invention it will be seen that changes and modifications of the foregoing specific disclosure may be made without dcparting from the spirit and scope of the invention.

What is claimed as new is:

1. In letoff mechanism for a loom having a warp which feeds forwardly during loom operation, a pneumatic cylinder, a piston therein, mechanism operatively connecting the piston and the warp, a pneumatic system creating pneumatic pressures within the cylinder causing the piston to exert a force through said mechanism tending to resist forward motion of the warp, and means to vary the pneumatic pressure in the system to vary the resistance offered by said mechanism to forward motion of the warp.

2. In letoff mechanism for a loom having a warp which feeds forwardly during loom operation, a pneumatic cylinder, a piston therein, mechanism operatively connecting the piston and the warp, a pneumatic system creating pneumatic pressures within the cylinder causing the piston to exert a force through said mechanism tending to resist forward motion of the warp, and a gauge indicating the pneumatic pressure in the system.

3. In letoff mechanism for a loom having a warp which feeds forwardly from a Warp beam which diminishes in diameter during loom operation, mechanism operatively connected to the warp by means of which forward movement of the warp can be controlled, a pneumatic system operatively connected to said mechanism causing the latter to resist forward movement of the warp, and means in said system by which the pneumatic force exerted by the system on said mechanism may be diminished as the diameter of the warp beam diminishes.

4. In letoff mechanism for a loom having a warp which feeds forwardly from a warp beam which diminishes in diameter during loom operation, a pneumatic cylinder, a piston therein, mechanism operatively connecting the piston and the Warp, means creating pneumatic pressure within the cylinder causing the piston to exert a force through said mechanism tending to resist forward movement of the warp, and means in said system by which the pneumatic force exerted by said system on said mechanism may be lessened as the diameter of the warp beam diminishes.

5. In letoff mechanism for a loom having a warp which feeds forwardly during loom operation, a loom driving motor which runs during loom operation, mechanism operatively connected to the warp, a pneumatic system dependent for the pneumatic pressures therein upon running of the motor and effective to cause the mechanism to exert a force on said warp resisting forward movement thereof when the motor is running, and a valv in said system open when the motor is running and moving when the motor stops to disconnect the cylinder pneumatically from the system.

6. In letofi mechanism for a loom having a warp which feeds forwardly and a motor which runs during loom operation and continues to run during periods of loom stoppage, mechanism operatively connected to the warp by which forward motion of the latter can be controlled, a pneumatic system operatively connected to said mechanism, and an air pump operated by the motor during operation thereof independently of loom operation creating pneumatic pressures in said system effective to cause the mechanism to exert a force on said warp resisting forward movement thereof.

7. In letoff mechanism for a loom having a warp which feeds forwardly during loom operation, the loom having a driving motor which runs during loom operation, mechanism operatively connected to the warp, a pneumatic system dependent for the pneumatic pressures therein upon running of the motor and including a piston in a cylinder effective to cause the mechanism to exert a force on said warp resisting forward movement thereof, and a valve in said system controlling passage of air in the system into and out of said cylinder, said valve being normally open during motor operation to connect the cylinder pneumatically to said system and closing when the motor stops to prevent passage of air between the system and the cylinder.

8. In letoif mechanism for a loom having a warp which feeds forwardly during loom operation, the loom having a driving motor which runs during loom operation and continues to run during periods of loom stoppage, a pneumatic cylinder, a piston in said cylinder, mechanism operatively connecting the warp and piston, a pneumatic system for the cylinder, an air pump operated by the motor during running thereof independently of loom operation to create pneumatic pressures in said system eifective to cause the piston to exert a force on said mechanism tending to cause the latter to resist forward movement of the warp, and a valve in said system between the air pump and cylinder normally open when the air pum is operating due to running of the motor but closing incident to stoppage of the motor to prevent loss of pneumatic pressure within the cylinder.

9. In letoif mechanism for a loom having a warp beam from which warp feeds forwardly during loom operation, an arcuate member concentric with the beam axis and moving forwardly with the beam during certain periods of loom o eration and moving rearwardly relatively to the beam during other periods of loom operation, a pneumatic cylinder in fixed position, a piston therein, operative connections between the piston and arcuate member wrapped partly around the latter, and means creating pneumatic pressures within the cylinder effective to cause the piston acting through said connections to resist forward movement of said member during said certain periods and exerting a force tending to move said member rearwardly during said other periods.

10. In letoff mechanism for a loom having a warp beam from which warp feeds forwardly over a whip roll movable backwardly and forwardly in the loom, the warp beam being held against rotation during recurring periods in which the whip roll moves forwardly and the warp beam turning during other recurring periods, a pneumatic cylinder, a piston therein, mechanism operatively connecting the piston to the whip roll, and means creating pneumatic pressures in the cylinder causing the piston to resist forward movement of the whip roll and moving the whip roll rearwardly during said other periods.

RICHARD G. TURNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 858,138 Atkins June 25, 1907 1,391,435 Weissenborn Sept. 20, 1921 1,516 892 Reed Nov. 25, 1924 2,305,421 Herard Dec. 15, 1942 2,375,316 Moessinger May 8, 1945 

